1. Field of the Invention
This invention relates to accelerometers of the type commonly used to monitor vibrations in industrial applications. More particularly, the invention relates to accelerometers intended for use in extremely rugged environments and exposed locations, where contact with hazardous industrial chemicals, mechanical shock and high levels of electromagnetic and radio frequency interference (EMI/RFI) are likely.
2. Description of Related Art
Accelerometers are widely used to monitor the vibration of electrical motors, pumps and the like in industrial applications, especially continuous production applications. Changes in the vibration levels, particularly in rotating machinery, provide an advance warning of problems such as excessive wear or an approaching bearing failure. With such warning, the problems can be dealt with during regularly scheduled maintenance periods and expensive unplanned shutdowns can be avoided.
In industrial applications of this type, accelerometers are exposed to numerous hazards. Accelerometers near pumps are often splashed by acids, coolants, caustic solvents, oils, hydraulic fluids or other industrial chemicals that over time migrate into a conventional accelerometer and cause it to fail.
Accelerometers monitoring electrical motors, or which are near industrial electrical equipment, are exposed to high levels of EMI/RFI noise that can seriously interfere with operation of the electrical components in the accelerometer. Interference may be radiated directly into the accelerometer or conducted in through the case and mounting bolts.
Ground loops are also a particular problem where grounded case accelerometers have been used. Attempts to alleviate such problems by isolation stud mounting (which electrically insulates the case of the accelerometer from the equipment being monitored) are often defeated in harsh environments as the exterior of the accelerometer and the isolation stud are contaminated over time by conductive industrial materials.
Finally, manufacturing facilities are a notoriously rough location for sensitive monitoring equipment. Accelerometers mounted on industrial machinery may be exposed to high G-force impacts and other physical abuse. The cables connected to the accelerometers may be inadvertently pulled excessively, or bent to very sharp angles, leading to premature failure.
Prior art accelerometers have proven to be deficient in the rugged environments described above. None have provided the necessary resistance to industrial chemicals and impact, EMI/RFI noise rejection and ground isolation in combination with high quality electronics, sensitivity, and ease of installation needed in the industrial environment.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a hermetically sealed accelerometer which has excellent resistance to most industrial chemicals in combination with ground isolation, EMI/RFI resistance and an integral cable with superior cable bend and strain relief protection.
A further object of the invention is to provide an accelerometer with the properties identified above that includes internal circuitry with a low impedance output.
Yet another object of the invention is to provide an accelerometer which is easy to mount. Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.